Free ForeverNo SignupStockout PreventionUpdated 2026

Reorder Point Calculator

Know exactly when to reorder each product — so you never stockout on best sellers or overstock slow movers.

Reorder point (ROP) = (Average Daily Sales × Lead Time Days) + Safety Stock. When your stock level hits the ROP, place a new order. Safety stock is your buffer against demand spikes and supplier delays — it's the cost of avoiding stockouts.

Average Daily Sales (Units)

Average units sold per day over the last 90 days

Supplier Lead Time (Days)

Days from order placed to stock received

Safety Stock (Days of Supply)

Buffer stock expressed as days of demand coverage

Unit CostOptional — shows safety stock value

Purchase cost per unit (for safety stock value)

The Formula

ROP = (Daily Sales × Lead Time) + (Daily Sales × Safety Days)

In plain English

ROP = (avg daily sales × lead time days) + safety stock units.

Worked Example

15 units/day × 14-day lead time = 210 units. + 15 × 7 days safety = 105. ROP = 315 units.

Setting Safety Stock Levels

Safety stock protects against two risks: demand variability (selling faster than forecast) and supply variability (supplier delivering late). The cost of a stockout — lost sales, customer disappointment, paid traffic wasted — usually exceeds the cost of holding a reasonable buffer.

Rule of thumb: safety stock = lead time × (max daily sales − avg daily sales). For stable demand, 7 days of safety stock is typical. For seasonal or viral products, increase to 14–21 days.

7–14 days

Typical safety stock for e-commerce

2–4 weeks

Typical supplier lead time

2–5%

Stockout rate target

3–5×

Revenue lost vs. safety stock cost when stocked out

Recommended Safety Stock by Category

Category	Min Safety Stock	Recommended	High-Risk
Fast-moving / hero SKUs	7 days	14 days	21 days
Standard SKUs	5 days	7–10 days	14 days
Slow-moving / long tail	0–3 days	3–5 days	7 days

Source: Shopify Inventory Management Guide · APICS Supply Chain Standards 2024

Common Mistakes

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Using average demand without considering variability

Average daily sales of 15 units may swing from 5 to 30 on different days. Safety stock should account for demand variability — use standard deviation of daily sales × z-score for more accurate buffers.

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Setting the same safety stock for all SKUs

Your hero SKU deserves 21 days of safety stock. A $10 accessory SKU needs 3 days. Calibrate safety stock to the cost of stockout × frequency, not a flat rule.

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Not updating reorder points when sales velocity changes

If a product goes viral or enters a promotion, daily sales can 5–10× overnight. Reorder points should be reviewed monthly and updated when trend changes are detected.